Process for adsorption

ABSTRACT

In a process for the separation of oxygen from a gas stream by adsorption, the improvement comprising using, as the adsorbent, a compound have the formula M x  [M&#39;(CN) 6  ] y   
     wherein M is an element having an atomic number of 21, 25 to 30, 39, 50, or 57 to 59; 
     M&#39; is an element having an atomic number from 24 to 27; and 
     x and y are positive whole numbers such that the sum of the valence of M times x plus the valence of [M&#39;(CN 6 )] times y is equal to zero.

TECHNICAL FIELD

This invention relates to a process for the adsorption of oxygen fromgas streams using a transition metal hexacyano compound as theadsorbent.

BACKGROUND ART

Gas separations utilizing solid adsorbent materials are well known,particularly those in which naturally occurring and synthetic zeolitesare used. The synthetic zeolites are especially adapted to gasseparations based on the size of the gas molecule.

A number of different synthetic zeolites have been formulated and arecommercially available for gas separations. For example, such molecularsieve adsorbent materials are commonly used to remove high boilingimpurities such as water vapor and carbon dioxide upstream of furtherprocessing. Such usage is common for pretreatment of natural gasfeedstocks and precleanup of air prior to cryogenic separation. Otherapplications include the upgrading of refinery process streams such asrecycle hydrogen streams. Additionally, other zeolites are commonly usedin adsorption processes to separate air. Such zeolites are utilized ineither pressure swing or temperature swing adsorption processes,although the pressure swing processes are generally preferred. Thesezeolites are typically nitrogen selective, that is, the nitrogencomponent of the air stream is adsorbed preferentially to the oxygencomponent. As a result, the nitrogen component is loaded onto theadsorbent bed whereas the oxygen component tends to remain in the gasphase. Although the zeolite molecular sieve adsorbent materials areeffective materials for separating air, they have one significantdrawback. That drawback is related to the fact that by nature of theirnitrogen selectivity, it is the major component of air that is adsorbedrather than the minor oxygen component. Since air composition isnominally 78 percent nitrogen, nitrogen selectivity for the adsorbentresults in large adsorbent material requirements for such a separationprocess. It would be advantageous, therefore, for a separation processto adsorb oxygen rather than nitrogen and thereby reduce the adsorbentmaterial requirements.

The potential advantage of oxygen selective processes has beenrecognized and, for this purpose, oxygen selective carbon-type molecularsieve adsorbents have been made available. This type of adsorbent israte selective, however. Consequently, these materials are necessarilyused in nonequilibrium process cycles that maximize sorption rates ofoxygen with respect to those of nitrogen. This, in turn, requires theuse of rapid cycles, for example, cycles of about one minute induration, which restricts cycle design to pressure swing adsorptionprocesses and have relatively high power requirements.

Thus, there is a need for adsorbent processes which are both oxygenselective and non-rate selective.

DISCLOSURE OF THE INVENTION

An object of this invention, then, is to provide a versatile adsorptionprocess advantageously adaptable to conventional pressure or temperatureswing separations.

Other objects and advantages will become apparent hereinafter.

According to the present invention, an improvement has been discoveredin a process for the separation of oxygen from a gas stream byadsorption. The improvement comprises using, as the adsorbent, acompound having the formula:

    M.sub.x [M'(CN).sub.6 ].sub.Y

wherein M is an element having an atomic number of 21, 25 to 30, 39, 50,or 57 to 59;

M' is an element having an atomic number from 24 to 27; and

x and y are positive whole numbers such that the sum of the valence of Mtimes x plus the valence of [M'(CN)₆ ] times y is equal to zero.

DETAILED DESCRIPTION

The transition metal hexacyano compounds defined above are, among otherthins, known pigments and catalysts as shown, for example, in U.S. Pat.Nos. 3,094,379 and 3,278,457, respectively. The characteristic of beingan oxygen selective adsorbent is not recognized, however. As will beapparent from the atomic numbers, M can be any of the elements includingscandium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, tin,lanthanum, cerium, or praseodymium and M' can be any of the elements,chromium, manganese, iron, or cobalt. The formula subscripts x and y arechosen to form neutral molecules.

Preferred adsorbent compounds are Zn₂ [Fe(CN)₆ ], Zn₃ [Fe(CN)₆ ]₂, andCe[Fe(CN)₆ ]. The Zn₂ [Fe(CN)₆ ] is characterized by good loading and ahigh separation factor although its gas adsorption rate is relativelylow. The Zn₃ [Fe(CN)₆ ]₂ compound is characterized by good loading andfast gas adsorption rates although its separation factor is moderate.The Ce[Fe(CN)₆ ] has a separation factor between those of the two zinccompounds, and its oxygen loading is much higher than those of eitherzinc compound. The rates of Ce[Fe(CN)₆ ] are similar to those of Zn₂[Fe(CN)₆ ]. The choice of adsorbent material will depend not only on theloading, ratio and separation factor, but also on the application.

The separation method can utilize a pressure swing adsorption processwhereby the oxygen-containing gas feed stream is contacted with theadsorbent bed material, which adsorbs at least some of the oxygencomponent and discharges an oxygen-depleted gas stream from theadsorbent bed. The adsorbent bed can be regenerated by reducing thepressure on the bed and thereby removing the oxygen-rich adsorbate. In asimilar fashion, adsorbent material can be utilized in temperature swingadsorption processes whereby the feed gas stream containing the oxygenis passed through the adsorbent bed at a low temperature allowing atleast some of the oxygen component to be adsorbed on the bed anddischarging an oxygen-depleted gas stream from the adsorbent bed. Theadsorbent bed can then be regenerated by raising the temperature of thebed to drive off the oxygen-rich adsorbate. Both the pressure swing andtemperature swing adsorption processes are, aside from the adsorbenttaught in this specification, conventional insofar as process steps areconcerned. Conventional process conditions can also be applied herealthough preferred conditions may vary somewhat with the feed gas andfrom those utilized with other adsorbents. Thus, with air as the feedgas in the pressure swing mode, pressures can be in the range of about0.01 atmosphere to about 100 atmospheres, but are preferably in therange of about 1 to about 30 atmospheres for adsorption with adsorbentregeneration being carried out at about atmospheric pressure. Thetemperature range for the pressure swing cycles is about 150° K. toabout 350° K. and is preferably in the range of about 290° K. to about340° K. In the temperature swing mode, temperatures can be in the rangeof about 195° K. to about 373° K. and are preferably in the range ofabout 273° K. to about 373° K. Optimum temperatures are about ambientfor adsorption and in the range of about 333° K. to about 366° K. foradsorbent regeneration. In general, all of the available adsorptionprocesses can be used together with the transition metal hexacyanocompounds defined above. Examples of this adsorption technology may befound in U.S. Pat. Nos. 2,944,627; 3,024,867; and 3,636,679.

The invention is illustrated by the following examples.

EXAMPLES

The physical properties of some hexacyano adsorbents are set forth inTable I.

The sorptive properties of the hexacyano compounds referred to hereinare determined by two types of experimental methods: (i) for individualgases, a gravimetric technique and (ii) for mixed gases, a volumetrictechnique.

The heart of the gravimetric system is the Sartorius pressuremicrobalance. The microbalance beam is a quartz rod suspended from andcontrolled by an electromechanical null balancing device. The beam,buckets, and suspension wires are enclosed in a stainless steel housingcapable of withstanding pressures of up to 2000 pounds per square inch(psi). The extreme sensitivity (0.1 microgram on the 1.4 milligramscale) and the small sample requirement (2.5 gram maximum load) make thegravimetric apparatus ideal for measuring single points for rapidscreening or for obtaining isotherms over a wide range of pressures.Signals from the null balancing device are presented in two ways. Adirect digital readout with automatic taring provides a running measureof the mass at any given time, and an analog record of mass as afunction of time provides a permanent record.

A further description of the gravimetric apparatus is as follows: themicrobalance scale is connected to a gas supply and a vacuum outlet.Control valves are used to regulate gas flow. Experimental data obtainedinclude gas pressure and temperature at the sample, as well as masschanges due to uptake or release of gas. The microbalance includes asteel housing that is partly enclosed in a temperature bath. The sampleis contained in a receptacle within the temperature bath whereas thesample counterweight is kept at ambient conditions.

The gas handling part of the gravimetric system is designed to provideknown gas pressures in the range of about 1 micron to about 500 psi.Superatmospheric pressures of individual gases are obtained fromcylinders through a manifold. Subatmospheric pressures are producedthrough a vacuum system that includes vapor traps as well as vacuumpumps. A controlled temperature environment is provided for the sampleside of the microbalance by three different devices. For temperatureswell above ambient, such as those used in activation, less than or equalto 250° C., a tube furnace is placed around the sample arm. Fortemperatures near ambient, the sample side is immersed in an oil bath.For temperatures well below ambient, cryogenic baths are used. Thetemperature of the sample is measured by a thermocoupled placed within 1centimeter of the sample bucket inside the sample chamber. Near ambient,the temperature can be controlled within ±0.5° C. and measured to within±0.1° C.

The balance is loaded with sample (about 0.5 gram) and counter-balancematerials through gasketed closures in the respective chanbers. Usually,nonporous glass beads serve as the counter-balance material. The sampleto be tested can be in powder or compacted form, e.g., crushed filtercake is often used after this material is screened through 20 onto 40mesh. After the chambers are closed, the system is carefully evacuatedat ambient temperature. Then, the sample temperature is raised undervacuum to some predetermined level to "activate" it for adsorption, thatis, to remove sorbed gases, vapors, or water of hydration, to preparethe sample for adsorption. Activation temperatures in the range of about100° to about 250° C. can be used. The most commonly used temperaturesare in the range of about 160° C. to about 190° C. After the samplereaches constant weight at the activation temperature, the sampletemperature is brought to the value desired for adsorption measurements.

Sorption measurements are most frequently made at constant temperature.The adsorption of gas is measured by admitting gas rapidly to some fixedpressure and following the increase in weight with time. Pressureequalization is usually achieved within 20 seconds; the time to reachadsorption equilibrium may require minutes or days. The constant weightcriterion is used with a slope of less than 2 micrograms in 5 minutesaccepted as "zero". The desorption of gas is measured in a similar wayby decreasing the pressure to some fixed value. Frequently, desorptionis performed by simply pumping on the sample. Tests for equilibriumvalues are usually made by repeating the point on adsorption after anintervening desorption from the value to be tested. However, occasionaltests are made by approaching the test value from both directions.Isobaric measurements have also been made by raising and lowering thesample temperature, but this is not as convenient as the isothermalpressure swing technique.

The pressures of interest here are greater than 10 torr, so thatthermomolecular effects need not be considered. However, as thepressures increase above values of 1 atmosphere, bouyancy effects mustbe considered in establishing the correct adsorbed weight. Thecounterbalance automatically corrects for most of the buoyancy when botharms of the balance are at the same temperature. When the sampletemperature is different from that of the counterbalance, differences ingas density magnify any difference in the volume of gas displaced. Tocalculate buoyancy effects, the sample is exposed to helium at the sametemperatures and pressures used in the isotherm measurements. From thedisplacements observed in helium, the corrections to the observedweights are determined after accounting for differences in molecularweight.

The volumetric system is used for adsorption measurements with gasmixtures such as synthetic air. These experiments involve three mainstages: (1) the establishment of equilibrium between a flowing gasmixture and a bed of activated adsorbent, (2) the retrieval of all thegas from the isolated equilibrated adsorbent bed, and (3) the analysesof the mixtures in the gas and adsorbed phases in the adsorber. Theapparatus has four main sections, identified by function. The adsorberitself is a stainless steel tube having a volume of about 33 cubiccentimeters fitted with porous frits to retain adsorbent material. It ismounted inside an oven (with forced air circulation) that providestemperatures from ambient to 343° C. within ±1° C. An internalthermocouple mounted on the adsorber axis can measure bed temperaturesto ±0.1° C.

The gas handling portion of the volumetric system is designed to providecontrolled, measured gas flows up to several hundred cubic centimetersper minute at pressures in the range of about 1 to about 7 atmospheres.Both helium and synthetic air are provided by the manifold, andchromatographic valves are employed to permit easy switching andsampling of the gas streams. To reduce dead space volumes, 1/16 inchdiameter stainless steel tubing is used. The third section of theapparatus is a manifold for cryopumping gas from the adsorber. mixingit, and providing it for analysis. The cryopump is simply a bulbcontaining activated silica gel, which has negligible adsorptivecapacity for either oxygen or nitrogen at ambient conditions. At liquidnitrogen temperature, silica gel is relatively nonselective and has highcapacities for both oxygen and nitrogen. By heating the adsorber andcooling the cryopump, essentially all of the gas in the adsorberisolated at equilibrium can be removed. For example, residual pressuresof about 1 to about 2 microns at about 100° C. to about 200° C. areeasily obtained. In the fourth section, the gas phase in the adsorber atequilibrium and the total gas pumped from the adsorber are analyzedchromatographically. A chromatograph, fitted with molecular sievezeolite columns, is used in conjunction with an integrator. Standardchromatographic techniques are employed. Estimates of the errors havebeen made from analyses of error sources and by measuring zeolites withknown properties. Total loading can be determined to within ±0.01millimol per gram or ±0.03 weight percent air. The composition of theadsorbed gases can be determined within ±0.0013 millimol per gram foreither oxygen or nitrogen, corresponding to an error in the separationfactor of ±0.02.

The method for the mixed gas experiments is as follows: powdered samplesof the material to be studied are first compacted to pressed chips (20to 40 mesh), weighed accurately, then loaded into the adsorber. Thesample is activated by passing helium gas through it at some elevatedtemperature, less than or equal to 250° C. The sample is then cooled tothe desired temperature, and the test gas (usually synthetic air) isanalyzed. The test gas at some fixed, known pressure is then passedthrough the adsorbent sample until equilibrium is achieved, i.e., whenthe compositions of the gas entering and leaving the adsorber areidentical. Then the adsorber is isolated, and the rest of the apparatusis prepared for the transfer and analysis of the gas from the adsorber.The total gas mixture is cryompumped from the adsorber (both the gasphase and the adsorbed phase). The cryopumped gas is warmed to ambienttemperature and analyzed. The amount and composition of the adsorbedphase are calculated by difference from the corresponding data for thetotal mixture and that contained in the gas phase at equilibrium. Afterthe adsorption measurements, the solid sample is removed from theadsorber and weighed again.

The adsorption of synthetic air (20.95 percent oxygen in nitrogen) ismeasured on a purchased sample of Co₂ [Fe(CN)₆ ].5H₂ O. The "asreceived" powder is pressed into discs at 5600 psi; these discs arebroken into chips and a mesh fraction through 20 onto 40 mesh isretained for testing. Adsorption data are measured after each of threeactivations performed with the sample in place. In each case, the samplechips are purged with flowing helium for 16 hours at temperatures of100°, 128°, and 132° C., respectively. The separation factor changedvery little with the extent of activation, but there were increases inthe loadings after the second activation. During the adsorption step,the approach to equilibrium was followed by analyzing the effluent gasfrom the adsorber. At the air flow rate used (30 cubic centimeters perminute), the time allowed for adsorption (1.5 hours) was more thansufficient to achieve equilibrium.

Gas adsorption data for some hexacyano compounds can be found in TableII. Adsorbent preparation and data can be found in Tables III throughVI.

Hydrated Zn₂ [Fe(CN)₆ ] polycrystalline powders have been prepared byseveral methods using various reagents and conditions. The most commonsynthesis is described below. Deviations from this "standard" procedureare mentioned in Table III under "Comments".

The standard synthesis is based on the precipitation of an insolublehydrate by rapid mixing of reagents soluble in an aqueous medium,specifically:

    2Zn(NO.sub.3).sub.2 +Ca.sub.2 [Fe(CN.sub.6 ]+xH.sub.2 O→Zn.sub.2 [Fe(CN.sub.6 ].xH.sub.2 O+2Ca(NO.sub.3).sub.2

Values of x=2 to 2.5 are typical of samples showing superior adsorptionperformance. Values of "x" are determined from the difference in weightof the sample in air-dried and vacuum-activated states. The standardreagents are Zn(NO₃)₂.6H₂ O and Ca₂ [Fe(CN)₆ ].(10 to 11)H₂ O in aqueoussolution at the concentrations 0.4M and 0.1M, respectively. Thedissolved salts are filtered before use. The volumes of these solutionsare 300 cubic centimeters and 150 cubic centimeters, respectively, sothat the ratio of moles Zn²⁺ to moles [Fe(CN)₆ ]⁴⁻ is kept at four timesthe stoichiometric value. Either deionized water (pH=5.5 to 6) or tapwater (pH=6.5 to 7) are used for these solutions, and the preparationsare performed at ambient temperature.

Precipitation occurs as streams of the reagent solutions are mixed inthe throat of a funnel. The precipitate is stirred in the mother liquoruntil it is filtered. After the initial filtration, the precipitate iswashed by blending with water, then it is filtered again. Ordinarilythree such washing-filtrations are performed. The final filter cake isdried in air for 16 hours at 50° C. For convenience, the dried filtercake is usually crushed and screened, and the -20+40 mesh fractionretained for adsorption testing.

An investigation of the effect of Ca₂ [Fe(CN)₆ ] source on sorptiveproperties is made. This reagent is obtained from three suppliers indifferent purities.

Hydrated Zn₃ [Fe(CN)₆ ]₂ polycrystalline powders are prepared usingapparatus the same as and techniques similar to those used in thepreparation of Zn₂ [Fe(CN)₆ ]. The standard synthesis is based on thefollowing chemistry:

    3Zn(NO.sub.3).sub.2 +2K.sub.3 [Fe(CN).sub.6 ]+xH.sub.2 O→Zn.sub.3 [Fe(CN).sub.6 ].sub.2.xH.sub.2 O+6KNO.sub.3,

where values of x less than 1 mole are typical. Specific values ofsynthesis variables and changes in the methods and conditions arepresented in Table IV. As indicated in Table IV, it is possible by slowdiffusion to prepare relatively large crystals (preparation #4) whoseadsorption rates are not significantly slower than the rates of samplescomposed of much smaller crystals. Samples prepared by "rapid mixing"use the same precipitation method as that for Zn₂ [Fe(CN)₆ ]. For"dropwise" addition, the anion reagent is added dropwise to a solutionof the cation reagent. "Slow diffusion" denotes a method in which theusual reagent solutions are separated by a water barrier through whichthe reacting ions diffuse to form the precipitate.

Hydrated crystals of Ce(III) [Fe(II)(CN)₆ ] are prepared byprecipitation and crystallization methods that are formally similar tothe syntheses for Zn₂ [Fe(CN)₆ ] and Zn₃ [Fe(CN)₆ ]₂. The synthesischemistry is based on:

    Ce(NO.sub.3).sub.3 +K.sub.3 [Fe(CN).sub.6 ]+xH.sub.2 O→Ce[Fe(CN).sub.6 ].xH.sub.2 O+3KNO.sub.3,

where values of x greater than or equal to 4.0 are typical.

Specific values of synthesis variables and comments on the methods andconditions are given in Table V. The precipitation/crystallization ratesfor Ce[Fe(CN)₆ ] are observably slower than those of the two Zncompounds, and the rates for Ce[Fe(CN)₆ ] decrease perceptibly fromrapid precipitation to slow crystallization as the reagentconcentrations decrease. Relatively large crystals are prepared easily.As indicated in Table V, the effect of Ce reagent purity and the effectof precipitation rate on adsorption performance are studied.

Hydrated hexacyanometalates other than Zn₂ [Fe(CN)₆ ], Zn₃ [Fe(CN)₆ ]₂,and Ce(III)[Fe(III)(CN)₆ ] are prepared as crystalline powders bymethods similar to those used for the two Zn compounds. The principle ofprecipitating an insoluble hydrate from an aqueous mixture of solublesalts is retained, but the chemistry has been modified to suit thevarious compositions. For example, divalent transition metalhexacyanometalate (III) compounds are synthesized according to thereaction:

    3MX.sub.2 +2K.sub.3 [M'(CN).sub.6 ]+xH.sub.2 O→M.sub.3 [M'(CN).sub.6 ].sub.2.xH.sub.2 O+6KX.

Here M is the divalent metal, M' is the metal in oxidation state (III),and X represents chloride or nitrate. Values of x vary considerably withM and M'. Reagents are chosen so that the ratio M/M' exceeds the valuecorresponding to stoichiometry. The general methods by which theprecipitates are obtained and comments specific to the individualpreparations are set out in Table VI.

The preparations in Table VI designated by quotation marks correspond toattempts to make mixed phase samples containing both [Fe(CN)₆ ]⁴⁻ and[Fe(CN)]₆ ]³⁻ ions. The preparations designated by "Zn₃ [Fe(CN)₆ ]₂ "are made by methods used for pure Zn₃ [Fe(CN)₆ ]₂ samples; thosedesignated "Zn₂ [Fe(CN)₆ ]" are made according to pure Zn₂ [Fe(CN)₆ ]methods. Both the "Zn₃ [Fe(CN)₆ ]₂ " and "Zn₂ [Fe(CN)₆ ]" preparationsexhibit O₂ selectivity, but the adsorptive properties are accounted forby physical mixture of pure phases observed in the x-ray diffractionpatterns of the mixtures.

The adsorbent materials require activation for use in either pressureswing or temperature swing adsorption separation processes. Suchactivation involves the removal of some water of hydration, which varieswith composition with values in the range 0.3 to 21 percent of theactivated weight. Activations can be accomplished by standard methodssuch as heating while purging the adsorbent with gas or vacuum pumpingof the adsorbent bed.

From the tabular summaries, it can be seen that many hexacyano compoundsof transition elements exhibit O₂ selectivity. Among those, fourcompounds show combinations of adsorbent properties of special practicalinterest. The Zn₂ [Fe(CN)₆ ] compound has good O₂ loadings (0.20 to 0.25mmol/g) and very low N₂ loadings that lead to the highest separationfactors for an air feed (11 to 120). The sorption rates are moderate, asindicated by the O₂ adsorption at 1000 torr (60 to 84 percent ofequilibrium in 10 minutes). The Zn₃ [Fe(CN)₆ ]₂ compound also has goodO₂ loadings, but the N₂ loadings are higher, so that lower separationfactors are obtained (1.36 to 1.75). The sorption rates are very fast(95 to 97 percent of equilibrium in 1 minute), comparable to those ofzeolites. The Co₂ [Fe(CN)₆ ] compound has similar rates (90 percent ofequilibrium in 1 minute) and higher separation factors (2 to 3), but theO₂ loading is about half those of the Zn compounds. Note that theseparation factor obtained with synthetic air (2.17) compares veryfavorably with the value (2.23) obtained with pure gases on the samesample. This experimental result is considered conclusive evidence ofthe O₂ selectivity of these adsorbents. The Ce(III)[Fe(III)(CN)₆ ]compound has very high O₂ loadings (0.42 to 0.56 mmol/g) and goodseparation factors (10 to 48 at 10 minutes). For this material, theseparation factor is calculated as a function of time, because thesorption of N₂ requires very long times to reach equilibrium (hours todays). The intrinsic O₂ sorption rates for Ce[Fe(CN)₆ ] (59 to 84percent of equilibrium in 10 minutes) are similar to those of Zn₂[Fe(CN)₆ ], but the uptake is about twice as high for the Ce compoundbecause the equilibrium loading is higher.

The data presented in Tables III to VI show that the sorptive propertiesof the hexacyano compounds for O₂ and N₂ depend on the method ofpreparation. From Table III, it can be seen that Zn₂ [Fe(CN)₆ ]materials having O₂ loadings and separation factors superior to those ofcommercial Zn₂ [Fe(CN)₆ ] (Table II) can be made, when the proper[Fe(CN)₆ ]⁴⁻ reagent solution is used. From Table IV, it is apparentthat the N₂ loading and separation factors of Zn₃ [Fe(CN)₆ ]₂ aresensitive to the purity of the reagents and the way in which they arebrought together for reaction. From Table V, it is evident thatCe[Fe(CN)₆ ] samples having the fastest O₂ uptakes are those prepared atthe lower reagent concentrations and with high Ce reagent purity.

                                      TABLE I                                     __________________________________________________________________________    PHYSICAL PROPERTIES OF SOME HEXACYANO ADSORBENTS                                                     BET N.sub.2                                                                         WEIGHT  HYDRATED                                                        SURFACE                                                                             LOST ON CRYSTAL                                  ACTIVATED              AREA  ACTIVATION                                                                            DENSITY                                  COMPOSITION                                                                            SOURCE        (M.sup.2 /G)                                                                        (Wt. %) (G/CM.sup.3)                             __________________________________________________________________________    Zn.sub.2 [Fe(CN).sub.6 ]                                                               *              29   17.35                                                     PREPARATION #14 (III)                                                                        58   13.99   1.78                                     Zn.sub.3 [Fe(CN).sub.6 ].sub.2                                                         PREPARATION #1 (IV)                                                                         664    1.69   1.50                                     Co.sub.2 [Fe(CN).sub.6 ]                                                               *             146   30.14   2.12                                     Co.sub.3 [Co(CN).sub.6 ].sub.2                                                         *             434   39.43   1.74                                     Cu.sub.3 [Co(CN).sub.6 ].sub.2                                                         PREPARATION #11 (VI)                                                                        399   21.22   1.79                                     __________________________________________________________________________     NOTES:                                                                        * indicates that the component is obtained from an outside commercial         source.                                                                       "Preparation #" or "Preparation number" indicate that the composition is      prepared as provided in this specification. Parenthetical expression          indicates Table number.                                                       M.sup.2 /G = square meters per gram.                                          Wt % = percent by weight                                                      G/CM.sup.3 = grams per cubic centimeter                                       BET = BrunauerEmmett-Teller and refers to the method of measuring surface     area pioneered by these men.                                             

                                      TABLE II                                    __________________________________________________________________________    GAS ADSORPTION DATA FOR HEXACYANO COMPOUNDS                                                     Adsorption Loading (mmol/g)           O.sub.2 Uptake                                N.sub.2             Separation  at 1000 Torr                        Temp                                                                              O.sub.2                                                                             1000                                                                             N.sub.2                                                                             Ar    CO.sub.2                                                                           Factor      (mmol/g)              Compound      (°C.)                                                                      1000 Torr                                                                           Torr                                                                             3779 Torr                                                                           1000 Torr                                                                           150 Torr                                                                           O.sub.2 /N.sub.2                                                                    In 1 Min.                                                                           In 10                 __________________________________________________________________________                                                            Min.                  Zn.sub.2 [Fe(CN).sub.6 ]                                                      *             23-28                                                                             0.157 0.014                                                                            0.046 0.021 0.459                                                                              12.9  (0.046)                                                                             0.094                 PREPARATION #1 (III)                                                                        22-23                                                                             0.238 0.004                                                                            0.016 0.005 0.504                                                                              56.1  0.066 0.167                 PREPARATION #4 (III)                                                                        22-23                                                                             0.233    0.021            41.9  0.077 0.171                 PREPARATION #14 (III)                                                                       23-25                                                                             0.239    0.027            33.4  0.073 0.194                 Zn.sub.3 [Fe(CN).sub.6 ].sub.2                                                PREPARATION #1 (IV)                                                                         22  0.210 0.145                                                                            0.467       0.416                                                                              1.70  0.204 0.210                 Co.sub.2 [Fe(CN).sub.6 ]                                                      *             22-23                                                                             0.110 0.058                                                                            0.191 0.096 0.261                                                                              2.17  0.100 0.108                                                                         (5 Min.)              *             22   0.099**  0.165**         2.28**                            Co.sub.3 [Co(CN).sub.6 ].sub.2                                                *             22-26                                                                             0.132 0.117                                                                            0.370 0.135 0.615                                                                              1.35  0.126 0.130                                                                         (8 Min.)              Cu.sub.3 [Co(CN).sub.6 ].sub.2                                                PREPARATION #11 (VI)                                                                        19-20                                                                             0.297 0.287                                                                            0.818 0.309 1.073                                                                              1.37                              Ce[Fe(CN).sub.6 ]                                                             PREPARATION #15 (V)                                                                         22-23                                                                             0.529    0.368            5.4   0.169 0.410                                   0.410    0.099            15.6                                                (10 min) (10 min)         (10 min)                          __________________________________________________________________________     NOTES:                                                                        mmol/g = millimoles per gram                                                  °C. = degrees Celcius                                                  Min. = minutes                                                                ** = refers to mixed gas adsorption data. The mixed gases are 21 percent      O.sub.2 in N.sub.2.                                                      

    TABLE III      ADSORBENT PREPARATION AND DATA (Zn.sub.2 [Fe(CN).sub.6 ])   AMOUNT     ADSORBED AT    AMBIENT TEMPERATURE REAGENT  (MMOL/G)  MOLE RATIO     N.sub.2 at CALCULATED PREPARATION Zn/Fe WATER COMMENTS, IF ANY, WITH     RESPECT TO REAGENTS, CONCENTRATIONS, O.sub.2 at 1000 torr 3779 Torr     SEPARATION NUMBER (STOICH. = 1) SOURCE METHODS, T, pH, DOPANTS, OR     ADDITIVES At Equil. In 10 Min. At Equil. FACTOR        1 2.5 De-Ionized  0.238 0.167 0.016 56.1  2 1.0 De-Ionized  0.205     0.159 0.070 11.0  3 2.5 Tap  0.225 0.173 0.022 38.6  4 4.0 Tap  0.233     0.171 0.021 41.9  5 2.5 Tap Ca.sub.2 [Fe(CN).sub.6 ] pH = 8 to 9 with     Ca(OH).sub.2 0.216 0.166 0.027 30.2  6 4.0 Tap Hexacyano Soln. Doped     with 3 mol % K.sub.3 [Co(CN).sub.6 ] 0.238 0.192 0.024 37.4  7 4.0 Tap     Ca.sub.2 [Fe(CN).sub. 6 ] Added Dropwise to Zn(NO.sub.3).sub.2 0.240     0.160 0.011 82.3  8 4.0 Tap PPT, Boiled 1.5 Hrs. in Mother Liquor 0.245     0.176 0.014 66.0  9 4.0 Tap Zn(NO.sub.3).sub.2 Doped with 3 mol %     Co(NO.sub.3).sub.2 0.229 0.182 0.025 34.6 10 4.0 Tap Mg.sub.2      [Fe(CN).sub.6 ] 0.244 0.155 0.008 115.1 11 4.0 Tap Hexacyano Soln.     Doped with 6 mol % K.sub.3 [Co(CN).sub.6 ] 0.227 0.190 ≧0.027     ≦31.7 12 4.25 De-Ionized 0.8 PPM CuCl.sub.2 Added to H.sub.2 O     Before use 0.241 0.183 0.015 61.8 13 1.7 Tap PPT. Boiled 20 Min. in     Mother Liquor 0.244 0.187 0.033 27.9 14 4.25 Tap  0.239 0.194 0.027 33.4     15 4.0 Tap Zn Soln. Doped with 10 mol % Cd(NO.sub.3).sub.2 0.235 0.128     0.013 68.2 16 4.0 Tap Mg.sub.2 [Fe(CN).sub.6 ]; PPT. Boiled in Mother     Liquor 1.75 Hrs. 0.218 0.175 0.063 13.0 17 4.0 Tap Zn Soln. Doped with     20 mol % Cd(NO.sub.3).sub.2 0.209 0.142 0.025 31.5 18 4.0 Tap PPT.     Washed with De-Ionized H.sub.2 O 0.231 0.185 0.024 36.3 19 4.25 Tap PPT.     Boiled in Mother Liquor 6 Hrs. 0.217 0.181 0.039 21.0 20 4.25 Tap Prepn.     Performed at 40° C. 0.217 0.131 0.014 58.5 21 4.25 Tap Reagents     Prepared at 0° C., Precipn. at 23-25° C. 0.191 0.145 0.006     120.1 22 4.0 Tap Water pH 5 By Adding HNO.sub.3 Before Use 0.226 0.161     0.022 38.8 23 4.0 Tap Mg.sub.2 [Fe(CN).sub.6 ] and ZnSO.sub.4 0.247     0.173 0.015 62.1 24 4.0 Tap Fluka Ca.sub.2 [Fe(CN).sub.6 ] + HNO.sub.3     to After Color Change; pH 6.5 0.236 0.150 0.013 68.4 25 3.9 Tap Mg.sub.2     [Fe(CN).sub.6 ]; Low: [Zn.sup.2+ ] = 0.129 M, [Fe(CN).sub.6.sup.4- ] =     0.033 M 0.230 0.161 0.011 78.9 26 4.0 "Decationized" H.sup.+ Substituted     for Cations in H.sub.2      O, pH 5 0.226 0.152 0.011 77.5 27 4.0 "Decationized" Same as 26, but     ZnSO.sub.4 and Mg.sub.2 [Fe(CN).sub.6 ] 0.236 0.128 0.012 74.2 28 4.0     De-Ionized But Tap H.sub.2 O for Ca.sub.2 [Fe(CN).sub. 6 ] Soln. 0.235     0.183 0.021 42.2 29 4.0 Tap ZnCl.sub.2 0.220 0.172 0.028 29.6 30 4.0     De-Ionized Ca.sub.2 [Fe(CN).sub.6 ] Soln. "Aged" 5 Days Before Use 0.216     0.182 ≦0.067  ≧12.2 31 4.0 Tap Ca.sub.2 [Fe(CN).sub.6 ]     Soln. "Aged" 6 Days Before Use 0.252 0.165 0.011 86.4 32 4.0 Tap Fluka     Ca.sub.2 [Fe(CN).sub.6 ] Soln. + CO.sub.2, Filtered, pH = 5.5 0.269     0.178 ≧0.014  ≦72.4 33 4.0 De-Ionized Ca.sub.2      [Fe(CN).sub.6 ] Soln. "Aged" 3 Days in Bright Light 0.255 0.163 0.010     96.2 34 4.0 De-Ionized Ca.sub.2 [Fe(CN).sub.6 ] Soln. "Aged" 4 Days in     Darkness 0.250 0.189 0.016 59.0 35 4.0 Tap DeGussa Ca.sub.2      [Fe(CN).sub.6 ] 0.195 0.155 ≧0.037       ≦19.6 36 1.0 De-Ionized K.sub.4 [Fe(CN).sub.6 ] and ZnSO.sub.4     0.107    0.097.sup.(a) 37 2.5 De-Ionized  0.131 0.068 0.044 11.2 38 1.5     De-Ionized PPT. Washed for Extensive Time in Blender 0.174 0.131 0.113     5.81 39 3.0 De-Ionized   0.050 40 2.5 De-Ionized Resin Beds Flushed for     20 Min. Before Use 0.149 0.102 0.048 11.7 41 3.0 Tap K.sub.4      [Fe(CN).sub.6 ]; ACS Certified Reagents 0.120 0.073 0.101 4.48 42 4.0     De-Ionized Water pH = 7 by Adding Ca(OH).sub.2 0.170 0.138 0.092 6.97 43     4.0 De-Ionized Ca.sub.2 [Fe(CN).sub.6 ] pH = 7 with Ca(OH).sub.2 ; Resin     Beds Flushed; Dry PPT.  0.126 44 4.0 Tap Zn Soln. Doped with 3 mol %     Cu(NO.sub.3).sub.2 0.149 0.106 0.077 7.30 45 4.25 De-Ionized 20 PPM     CaCO.sub.3 Added to Water Before Use 0.180 0.141 0.093 7.30 46 4.0 Tap     Hexacyano Soln. Doped with 3 mol % K.sub.3 [Fe(CN).sub.6 ] 0.118  0.075     5.94 47 0.75 Tap Ca.sub.2 [Fe(CN).sub.6 ]      Added Dropwise to Zn(NO.sub.3).sub.2 0.124   0.087.sup.(b) 0.271 1.73     48 4.25 De-Ionized 0.8 PPM CuCl.sub.2 Added to Water Before Use 0.151     0.064 8.90 49 1.72 Tap High Reagent Concns: [Zn.sup.2+ ] =      1.4, [Fe(CN).sub.6.sup.4- ] = 0.4 ≧0.112   0.186 ≧2.27 50     1.72 Tap Same as 49 but Solns. Mixed by Slow Diffusion ≧0.148     ≧0.140  (3.99) 51 4.0 Distilled Water Boiled Before Use 0.118     0.041 10.85 52 4.0 De-Ionized 36 PPM NaCl + 42 PPM MgSO.sub.4 + H.sub.2     O Before Use   0.154.sup.(c)    0.056.sup.(c) 10.38.sup.(c) 53 4.0 Tap     Fluka Ca.sub.2 [Fe(CN).sub.6 ] + HNO.sub.3 to Color Change 0.093     0.030.sup.(b) 54 4.0 Tap Fluka Ca.sub.2 [Fe(CN).sub.6 ] + HNO.sub.3 to     Before Color Change 0.092   0.030.sup.(b) 0.072 4.82 55 4.25 Tap H.sub.4     [Fe(CN).sub.6 ]; PPT into Ca(OH).sub.2 0.144 0.106 0.061 8.91 56 4.0 Tap     Zn(C.sub.2 H.sub.3      O.sub.2).sub.2 0.110 0.091 0.052 7.98 57 2.0 De-Ionized K.sub.4     [Fe(CN).sub.6 ]; PPT. Not Washed After Filtration 0.015    0.009.sup.(a)     58 2.0 De-Ionized ZnSO.sub.4 and K.sub.4 [Fe(CN).sub.6 ] 0.0        0.0.sup.(a) 59 2.0 De-Ionized ZnCl.sub.2 0.0   0.0.sup.(a) 60 2.0     De-Ionized K.sub.4 [Fe(CN).sub.6 ] 0.066   1.87 31 4.0 Tap Ca.sub.2     [Fe(CN).sub.6 ] Soln. "Aged" 6 Days Before Use 0.252 0.165 0.011 86.4 32     4.0 Tap Fluka Ca.sub.2 [Fe(CN).sub.6 ] Soln. + CO.sub.2, Filtered, pH =     5.5 0.269 0.178 ≧0.014  ≦72.4 33 4.0 De-Ionized Ca.sub.2     [Fe(CN).sub.6 ] Soln. "Aged" 3 Days in Bright Light 0.255 0.163 0.010     96.2 34 4.0 De-Ionized Ca.sub.2 [Fe(CN).sub.6 ] Soln. "Aged" 4 Days in     Darkness 0.250 0.189 0.016 59.0 35 4.0 Tap DeGussa Ca.sub.2      [Fe(CN).sub.6 ] 0.195 0.155 ≧0.037       ≦19.6 36 1.0 De-Ionized K.sub.4 [Fe(CN).sub.6 ] and ZnSO.sub.4     0.107    0.097.sup.(a) 37 2.5 De-Ionized  0.131 0.068 0.044 11.2 38 1.5     De-Ionized PPT. Washed for Extensive Time in Blender 0.174 0.131 0.113     5.81 39 3.0 De-Ionized   0.050 40 2.5 De-Ionized Resin Beds Flushed for     20 Min. Before Use 0.149 0.102 0.048 11.7 41 3.0 Tap K.sub.4      [Fe(CN).sub.6 ]; ACS Certified Reagents 0.120 0.073 0.101 4.48 42 4.0     De-Ionized Water pH = 7 by Adding Ca(OH).sub.2 0.170 0.138 0.092 6.97 43     4.0 De-Ionized Ca.sub.2 [Fe(CN).sub.6 ] pH = 7 with Ca(OH).sub.2 ; Resin     Beds Flushed; Dry PPT.  0.126 44 4.0 Tap Zn Soln. Doped with 3 mol %     Cu(NO.sub.3).sub.2 0.149 0.106 0.077 7.30 45 4.25 De-Ionized 20 PPM     CaCO.sub.3 Added to Water Before Use 0.180 0.141 0.093 7.30 46 4.0 Tap     Hexacyano Soln. Doped with 3 mol % K.sub.3 [Fe(CN).sub.6 ] 0.118  0.075     5.94 47 0.75 Tap Ca.sub.2 [Fe(CN).sub.6 ]      Added Dropwise to Zn(NO.sub.3).sub.2 0.124   0.087.sup.(b) 0.271 1.73     48 4.25 De-Ionized 0.8 PPM CuCl.sub.2 Added to Water Before Use 0.151     0.064 8.90 49 1.72 Tap High Reagent Concns: [Zn.sup.2+ ] =      1.4, [Fe(CN).sub.6.sup.4- ] = 0.4 ≧0.112   0.186 ≧2.27 50     1.72 Tap Same as 49 but Solns. Mixed by Slow Diffusion ≧0.148     ≧0.140  (3.99) 51 4.0 Distilled Water Boiled Before Use 0.118     0.041 10.85 52 4.0 De-Ionized 36 PPM NaCl + 42 PPM MgSO.sub.4 + H.sub.2     O Before Use   0.154.sup.(c)    0.056.sup.(c) 10.38.sup.(c) 53 4.0 Tap     Fluka Ca.sub.2 [Fe(CN).sub.6 ] + HNO.sub.3 to Color Change 0.093     0.030.sup.(b) 54 4.0 Tap Fluka Ca.sub.2 [Fe(CN).sub.6 ] + HNO.sub.3 to     Before Color Change 0.092   0.030.sup.(b) 0.072 4.82 55 4.25 Tap H.sub.4     [Fe(CN).sub.6 ]; PPT into Ca(OH).sub.2 0.144 0.106 0.061 8.91 56 4.0 Tap     Zn(C.sub.2 H.sub.3      O.sub.2).sub.2 0.110 0.091 0.052 7.98 57 2.0 De-Ionized K.sub.4     [Fe(CN).sub.6 ]; PPT. Not Washed After Filtration 0.015    0.009.sup.(a)     58 2.0 De-Ionized ZnSO.sub.4 and K.sub.4 [Fe(CN).sub.6 ] 0.0        0.0.sup.(a) 59 2.0 De-Ionized ZnCl.sub.2 0.0   0.0.sup.(a) 60 2.0     De-Ionized K.sub.4 [Fe(CN).sub.6 ] 0.066   1.87 61 0.5 De-Ionized  0.0     0.0  62 2.0 De-Ionized PPT. Aged in Mother Liquor 91 Hrs. Before     Filtering 0.004  0.0.sup.(a) 63 2.0 De-Ionized PPT. Filtered Immediately     0.061 0.054 0.073 3.17 64 2.0 De-Ionized  0.014 0.009 65 1.5 De-Ionized     Blender Not Used for Washing PPT. 0.010 0.006 66 3.0 De-Ionized Na.sub.4     [Fe(CN).sub.6 ], Lit. Meth., PPT. Boiled 0.003 0.002 67 2.5 De-Ionized     0.006 68 3.0 Tap Na.sub.4 [Fe(CN).sub.6 ], Lit. Meth., PPT. Boiled     <0.001.sup.(d)  <0.001.sup.(d) 69 4.0 Tap Hexacyano Soln. Doped with 3     mol % K.sub.3 [Cr(CN).sub.6 ] 0.0   0.0  70 4.0 Tap Zn Soln. Doped with     10 mol % Ce(NO.sub.3).sub.3 0.056  0.071 2.98 71 4.0 Tap Zn Soln. Doped     with 10 mol % AgNO.sub.3  0.033 .sup. 0.037.sup.(e) 72 4.0 De-Ionized     Water Boiled Before Use .sup. 0.054.sup.(f)  .sup. 0.011.sup.(f) 73 4.0     De-Ionized 57 PPM CaSO.sub.4 added to H.sub.2 O Before Use 0.066     ≧0.056  ≦4.45 74 4.25 Tap Prepn. Performed at 0° C.     0.0   0.0  75  Tap Min. Vol. H.sub.2 O Solns. Mixed with Glycerol, Then     PPTD. 0.071  0.105 2.55 76 4.0 "De-Anionized" OH.sup.-  for Anions,     HNO.sub.3 Added to pH = 6 0.033 0.015 0.028 4.45 77   Zn(NO.sub.3).sub.2     in CH.sub.3 OH + Ca.sub.2 [Fe(CN).sub.6 ] + H.sub.2 O 0.048 0.044 0.077     2.35     NOTES FOR TABLES III TO VI:     STOICH. or Stoich. = stoichiometry     MMOL/G = millimoles gas per gram adsorbent     Equil. = equilibrium     Soln. = solution     % = percent     PPM = parts per million     Prepn. = preparation     Precipn. = precipitation     Fluka = Tridom/Fluka Chemical Incorporated     M = molar     DeGussa = DeGussa Corporation     atm = atmospheres     Molycorp = Union Molycorp     ACS = American Chemical Society     Hrs. = hours     Min. Vol. = minimum volume     PPT = precipitated     T = time     .sup.(a) At 1000 Torr     .sup.(b) In 1 Minute     .sup.(c) For White Part of Dry Filter Cake      .sup.(d) In First 5 Minutes     .sup.(e) In 10 Minutes     .sup.(f) After 55 Minutes

                                      TABLE IV                                    __________________________________________________________________________     ADSORBENT PREPARATION AND DATA (Zn.sub.3 [Fe(CN).sub.6 ].sub.2)              __________________________________________________________________________                 CATION/ANION                                                                  REAGENT RATIO     REAGENT TREATMENT                              PREPN.                                                                              WATER  OF MOLES OF CONCEN-                                                                             ADDITON OF                                     NUMBER                                                                              SOURCE (STOICH. = 1.0)                                                                        TRATIONS METHOD  PRECIPITATE                            __________________________________________________________________________     1    Tap    1.3      1.0      Dropwise                                                                              Not Boiled                              2    Tap    4.0      4.0      Rapid Mix                                                                             Not Boiled                              3    Tap    1.3      1.0      Dropwise                                                                              Not Boiled                              4    Tap    1.3      1.0      Slow Diffusion                                                                        Not Boiled Large Crystals               5    Tap    2.5      2.5      Rapid Mix                                                                             Boiled                                  6    Tap    1.3      1.0      Dropwise                                                                              Boiled                                  7    Tap    1.3      1.0      Dropwise                                                                              Boiled                                  8    Tap    2.5      2.5      Rapid Mix                                                                             Boiled                                  9    Tap    2.5      2.5      Rapid Mix                                                                             Boiled                                 10    Tap    2.5      2.5      Rapid Mix                                                                             Boiled                                 11    Tap    2.5      2.5      Rapid Mix                                                                             Boiled                                 12    Tap    2.5      2.5      Rapid Mix                                                                             Boiled                                 13    De-ionized                                                                           1.3      1.0      Dropwise                                                                              Boiled                                 14    De-ionized                                                                           1.3      1.0      Dropwise                                                                              Boiled                                 15    Tap    1.3      1.0      Dropwise                                                                              Boiled                                 16    De-ionized                                                                           1.3      1.0      Rapid Mix                                                                             Boiled                                 17    De-ionized                                                                           1.3      1.0      Rapid Mix                                                                             Boiled                                 18    De-ionized                                                                           1.3      1.0      Dropwise                                                                              Boiled                                 19    De-ionized                                                                           1.3      4.2      Dropwise                                                                              Boiled                                 10    De-ionized                                                                           3.9      6.0      Rapid Mix                                                                             Boiled                                 21    De-ionized                                                                           1.3      2.0      Dropwise                                                                              Boiled                                 __________________________________________________________________________                           AMOUNT (MMOL/G) ADSORBED AT                                                  AMBIENT TEMP.                                                                               N.sub.2 AT                                                                           CALCULATED                         PREPN.                O.sub.2 AT 1000 TORR                                                                        3779 TORR                                                                            SEPARATION                         NUMBER                                                                              COMMENTS        AT EQUIL.                                                                            AT (T) MIN.                                                                          AT EQUIL.                                                                            FACTOR                             __________________________________________________________________________     1                    0.210    0.208 (2.5)                                                                        0.467  1.70                                2                    0.176   0.176 (10)                                                                          0.432  1.53                                3                    0.225    0.220 (2.5)                                                                        0.494  1.75                                4                    0 196  0.189 (1)                                                                            0.473  1.56                                5                    0.208  0.199 (1)                                                                            0.464  1.69                                6    Zn(NO.sub.3) doped with 3 mol %                                                               0.204  0.194 (1)                                                                            0.476  1.62                                     MnSO.sub.4                                                               7    K.sub.3 [Fe(CN.sub.6 ] doped with 3 mol %                                                     0.209  0.199 (1)                                                                            0.464  1.70                                     K.sub.3 [Co(CN).sub.6 ]                                                  8    Zn(NO.sub.3).sub.2 doped with 1 mol %                                                         0.215  0.208 (1)                                                                            0.497  1.63                                     Cu(NO.sub.3).sub.2                                                       9    Zn(NO.sub.3).sub.2 doped with 3 mol %                                                         0.213  0.206 (1)                                                                            0.516  1.56                                     Cu(NO.sub.3).sub.2                                                      10    Zn(NO.sub.3).sub.2 doped with 10 mol %                                                        0.209  0.200 (1)                                                                            0.605  1.30                                     Cu(NO.sub.3).sub.2                                                      11    Zn(NO.sub.3).sub.2 doped with 3 mol %                                                         0.192    0.189 (2.5)                                                                        0.529  1.37                                     Ni(NO.sub.3).sub.2                                                      12    Zn(NO.sub.3).sub.2 doped with 10 mol %                                                        0.191  0.182 (1)                                                                            0.529  1.36                                     Ni(NO.sub.3).sub.2                                                      13    Rapid Stirring  0.206  0.197 (1)                                                                            0.467  1.66                               14    Rapid Stirring  0.212  0.202 (1)                                                                            0.708  1.13                               15    Rapid Stirring  0.217  0.208 (1)                                                                            0.681  1.20                               16    Rapid Stirring  0.213  0.203 (1)                                                                            0.585  1.37                               17    Slow Stirring   0.211  0.203 (1)                                                                            0.530  1.50                               18    Slow Stirring   0.208  0.200 (1)                                                                            0.576  1.36                               19    Slow Stirring   0.204  0.196 (1)                                                                            0.465  1.65                               20    Slow Stirring   0.204  0.201 (1)                                                                            0.536  1.47                               21    Slow Stirring   0.215  0.207 (1)                                                                            0.448  1.66                               __________________________________________________________________________

                                      TABLE V                                     __________________________________________________________________________    ADSORBENT PREPARATION AND DATA (Ce[Fe(CN).sub.6 ])                            __________________________________________________________________________    REAGENT                                                                       MOLE RATIO                COMMENTS                                            PREPN.                                                                              Ce/Fe    CONCENTRATIONS                                                                           PRECIPITATION                                                                            ALL PREPARATIONS USE FISHER                                                   PURIFIED                                 NUMBER                                                                              (STOICH. = 1.0)                                                                        [Ce].sup.3+                                                                       [Fe(CN).sub.6 ].sup.3-                                                               RATE       Ce(NO.sub.3).sub.3 UNLESS STATED                                              OTHERWISE                                __________________________________________________________________________     1    2.0      0.6M                                                                              0.3M   Slow       De-ionized H.sub.2 O used for all                                             prepn's, large crystals                   2    3.0      0.9M                                                                              0.3M   Slow       Large Crystals                            3    1.0      0.3M                                                                              0.3M   Slow       Crystals obtained by evaporation          4    2.0      0.6M                                                                              0.3M   Slow       Large Crystals                            5    2.0      0.6M                                                                              0.3M   Slow       50% (Ce(NO.sub.3).sub.3 solution                                              from                                                                          Molycorp (Bastnasite),                                                        large crystals                            6    2.0      0.6M                                                                              0.3M   Slow       95% Ce(NO.sub.3).sub.3 solution from                                          Molycorp,                                                                     large crystals                            7    2.0      0.6M                                                                              0.3M   Slow       10x scale-up of #1, large crystals,                                           3% yield                                  8    --       --  --     --         #7 re-washed and re-tested                9    --       --  --     Slow       Second crop yield from #7 by                                                  evapora-                                                                      tion, large crystals, 23% yield          10    2.0      2.0M                                                                              1.0M   Rapid      50% Ce(NO.sub.3).sub.3 Molycorp                                               solution,                                                                     fine crystals                            11    2.0      2.0M                                                                              1.0M   Rapid      95% Ce(NO.sub.3).sub.3 Molycorp                                               solution,                                                                     fine crystals                            12    2.0      0.6M                                                                              0.3M   Slow       10x scale-up of #1, large crystals,                                           31% yield                                13    --       --  --     Slow       Second crop from #12 by                                                       evaporation,                                                                  large crystals, 36% yield                14    2.0      2.0M                                                                              1.0M   Rapid      Fine crystals                            15    2.0      0.6M                                                                              0.3M   Slow       20x scale-up of #1, large crystals,                                           17% yield                                16    --       --  --     Slow       Second crop from #15 by                                                       evaporation,                                                                  large crystals, 34% yield                17    2.0      0.6M                                                                              0.3M   Slow       99.9% Ce(NO.sub.3).sub.3 Molycorp                                             solution, large crystals                 18    2.0      2.0M                                                                              1.0M   Rapid      99.9% Ce(NO.sub.3).sub.3 Molycorp                                             solution, fine crystals                  19    2.0      0.6M                                                                              0.3M   Slow       10x scale-up of #1, large crystals,                                           no washing, 21.7% yield                  20    --       --  --     Slow       Second crop from #19 by                                                       evaporation,                                                                  large crystals, 18%                      __________________________________________________________________________                                         yield                                                                  AMOUNT (MMOL/G) ADSORBED AT                                                                           CALCULATED                                             AMBIENT TEMP.          SEPARATION                                      PREPN.                                                                              O.sub.2 AT 1000 TORR                                                                        N.sub.2 AT 3779                                                                         FACTOR                                          NUMBER                                                                              AT EQUIL.                                                                            AT 10 MIN.                                                                           AT 10 MIN.                                                                              AT 10                   __________________________________________________________________________                                                          MIN.                                             1    0.563  0.378  0.069     20.6                                             2    0.483  0.367  0.100     13.8                                             3    0.535  0.418  0.116     13.6                                             4    0.424  0.315  0.086     13.8                                             5    0.488  0.294  0.063     17.5                                             6    0.539  0.389  0.097     15.1                                             7    0.511  0.427  0.115     10.4                                             8    0.544  0.391  0.099     14.9                                             9    0.558  0.445  0.113     14.8                                            10    0.498  0.232  0.018     47.6                                            11    0.490  0.298  0.061     18.4                                            12    0.558  0.424  0.110     14.5                                            13    0.555  0.423  0.101     15.8                                            14    0.525  0.206  0.032     24.3                                            15    0.529  0.410  0.099     15.6                                            16    0.554  0.397  0.098     14.3                                            17    0.549  0.403  0.088     17.3                                            18    0.521  0.307  0.035     33.1                                            19    0.551  0.343  0.077     16.8                                            20    0.478  0.375  0.099     14.3                    __________________________________________________________________________     NOTE: Fisher Purified Ce(NO.sub.3).sub.3 is a salt sold by the Fisher         Scientific Company designated as purified.                               

                                      TABLE VI                                    __________________________________________________________________________     ADSORBENT PREPARATION AND DATA (VARIOUS METAL HEXACYANOMETALATES)            PREPARATION PROCEDURES                                                                                                AMOUNT (MMOL/G)                                                               ADSORBED AT                                                                   AMBIENT TEMP.   CALCU-                                                                   N.sub.2                                                                            LATED                                                                    3779 SEPARA-                          Prep.                        O.sub.2 at 1000                                                                          Torr TION                  Composition                                                                              #   Method  Comments         at Equil.                                                                          at (T) Min.                                                                         at Equil.                                                                          FACTOR                __________________________________________________________________________    Ca.sub.2 [Fe(CN).sub.6 ]                                                                 *                            0.000                                 Mn.sub.2 [Fe(CN).sub.6 ]                                                                 *           Second Activation; N.sub.2 Pressure                                                            0.032      0.026                                             1000 Torr                                              Fe.sub.4 [Fe(CN).sub.6 ].sub.3                                                           *                            0.114      0.059                                                                              7.24                  Co.sub.2 [Fe(CN).sub.6 ]                                                                 *                            0.110                                                                              0.109 (5)                                                                           0.191                                                                              2.17                  Co.sub.2 [Fe(CN).sub.6 ]                                                                 *           Mixed-Gas Adsorption: 20.95% O.sub.2                                                           0.099      0.165                                                                              2.28                                         in N.sub.2, 6.2 atm                                    Co.sub.2 [Fe(CN).sub.6 ]                                                                  1  Rapid Mixing                                                                          Co/Fe = 4.0, Tap H.sub.2 O                                                                     0.017                                                                              0.017 (10)                                                                          0.031                                                                              2.0                   Co.sub.2 [Fe(CN).sub.6 ]                                                                  2  Rapid Mixing                                                                          Co/Fe = 4.0, Tap H.sub.2 O                                                                     0.046                                                                              0.042 (1)                                                                           0.061                                                                              2.9                   Ni.sub.2 [Fe(CN).sub.6 ]                                                                 *           Gas Pressures = 300 Torr;                                                                      0.029      0.005                                             Irreversible Sorption                                  Cu.sub.2 [Fe(CN).sub.6 ]                                                                 *                            0.140      0.420                                                                              1.26                  Zn.sub.2 [Fe(CN).sub.6 ]                                                                 *           Chips (20 to 40 Mesh) from                                                                     0.157                                                                              0.098 (10)                                                                          0.051                                                                              12.9                                         Pressed Discs                                          Zn.sub.2 [Fe(CN).sub.6 ]                                                                 *           Powder (Same as lot above)                                                                     0.164      0.043                                                                              14.5                  Cd.sub.2 [Fe(CN).sub.6 ]                                                                 *                            0.006      0.013                                                                              1.6                   Cs.sub.4 [Fe(CN).sub.6 ]                                                                 *                            0.000      0.000                      Ba.sub.2 [Fe(CN).sub.6 ]                                                                 *                            0.000      0.000                      Pb.sub.2 [Fe(CN).sub.6 ]                                                                 *                            0.000                                 Cu.sub.3 [Fe(CN).sub.6 ].sub.2                                                            3  Rapid Mixing                                                                          (Cu + Zn)/Fe = 2.5, Tap H.sub.2 O,                                                             0.168                                                                              0.163 (1)                                                                           0.494                                                                              1.29                                         Precipitate Boiled                                     Cu.sub.2.4 Zn.sub.0.6 [Fe(CN).sub. 6 ].sub.2                                              4  Rapid Mixing                                                                          (Cu + Zn)/Fe = 2.5, Tap H.sub.2 O,                                                             0.165                                                                              0.161 (1)                                                                           0.494                                                                              1.26                                         Precipitate Boiled                                     Co.sub.2.6 Zn.sub.0.4 [Fe(CN).sub.6 ].sub.2                                               5  Rapid Mixing                                                                          (Co + Zn)/Fe = 2.5, Tap H.sub.2 O,                                                             0.157                                                                              0.151 (1)                                                                           0.416                                                                              1.42                                         Precipitate Boiled                                     Co.sub.1.8 Zn.sub.1.2 [Fe(CN).sub.6 ].sub.2                                               6  Rapid Mixing                                                                          (Co + Zn)/Fe = 2.5, Tap H.sub.2 O,                                                             0.148                                                                              0.139 (1)                                                                           0.377                                                                              1.48                                         Precipitate Boiled                                     K.sub.3 [Co(CN).sub.6 ]                                                                  *           Crystals Ground to Powder;                                                                     0.000      0.000                                             N.sub.2 Pressure = 1000 Torr                           Mn.sub.3 [Co(CN).sub.6 ].sub.2                                                            7  Rapid Mixing                                                                          Mn/Co = 3.0, De-Ionized H.sub.2 O                                                              0.191                                                                              0.191 (17)                                                                          0.616                                                                              1.17                  Fe.sub.3 [Co(CN).sub.6 ].sub.2                                                            8  Rapid Mixing                                                                          Fe/Co = 3.0, De-Ionized H.sub.2 O                                                              0.159                                                                              0.159 (33)                                                                          0.348                                                                              1.72                  Fe[Co(CN).sub.6 ]                                                                         9  Rapid Mixing                                                                          Fe/Co = 3.0, De-Ionized H.sub.2 O                                                              0.045                                                        Slow Precipitation; Slow Rates                         Co.sub.3 [Co(CN).sub.6 ].sub.2                                                           *                            0.132                                                                              0.132 (8)                                                                           0.370                                                                              1.35                  Ni.sub.3 [Co(CN).sub.6 ].sub.2                                                           10  Rapid Mixing                                                                          Ni/Co = 3.0, De-Ionized H.sub.2 O                                                              0.200                                                        Rates Slow and Irreproducible                          Cu.sub.3 [Co(CN).sub.6 ].sub.2                                                           11  Rapid Mixing                                                                          Cu/Co = 4.5, De-Ionized H.sub.2 O                                                              0.297                                                                              0.297 (27)                                                                          0.818                                                                              1.37                  Cu.sub.3 [Co(CN).sub.6 ].sub.2                                                           12  Rapid Mixing                                                                          Cu/Co = 4.5, De-Ionized H.sub.2 O                                                              0.295                                                                              0.295 (20)                                                                          0.837                                                                              1.33                                         (Repeat of #57)                                        Cu.sub.3 [ Co(N).sub.6 ].sub.2                                                           13  Slow Diffusion                                                                        Cu/Co = 4.5, De-Ionized H.sub.2 O                                                              0.27       0.20 (a)                                          Larger Crystals, Slow Rates                            Zn.sub.3 [Co(CN).sub.6 ].sub.2                                                           14  Rapid Mixing                                                                          Zn/Co = 2.37, De-Ionized H.sub.2 O                                                             0.173                                                                              0.173 (13)                                                                          0.492                                                                              1.29                  Mn.sub.3 [Cr(CN).sub.6 ].sub.2                                                           15  Rapid Mixing                                                                          Mn/Cr = 3.0, De-Ionized H.sub.2 O                                                              0.165                                                                              0.165 (9)                                                                           0.491                                                                              1.27                  Fe.sub.3 [Cr(CN).sub.6 ].sub.2                                                           16  Rapid Mixing                                                                          Fe/Cr = 3.0, De-Ionized H.sub.2 O                                                              0.184                                                                              0.121 (10)                                                                          0.253                                                                              2.74                                         O.sub.2 Slow                                           Ni.sub.3 [Cr(CN).sub.6 ].sub.2                                                           17  Rapid Mixing                                                                          Ni/Cr = 3.0, De-Ionized H.sub.2 O                                                              0.18 0.08 (10)                                                                           0.17 4                                            O.sub.2 Slow                                           Cu.sub.3 [Cr(CN).sub.6 ].sub.2                                                           18  Rapid Mixing                                                                          Cu/Cr = 3.0, De-Ionized H.sub.2 O                                                              0.05 0.05 (10)                                                                           0.124                                                                              1.5                   Zn.sub.3 [Cr(CN).sub.6 ].sub.2                                                           19  Rapid Mixing                                                                          Zn/Cr = 3.0, De-Ionized H.sub.2 O                                                              0.152                                                                              0.150 (2.5)                                                                         0.424                                                                              1.35                  Co.sub.3 [Mn(CN).sub.6 ].sub.2                                                           20  Rapid Mixing                                                                          Co/Mn = 3.0, Tap H.sub.2 O                                                                     0.128                                                                              0.121 (1)                                                                           0.321                                                                              1.50                  Zn.sub.3 [Mn(CN).sub.6 ].sub.2                                                           21  Rapid Mixing                                                                          Zn/Mn = 3.0, Tap H.sub.2 O                                                                     0.137                                                                              0.133 (1)                                                                           0.374                                                                              1.38                  "Zn.sub.3 [Fe(CN).sub.6 ].sub.2 "                                                        22  Rapid Mixing                                                                          Zn/Fe = 2.5, Tap H.sub.2 O, Precipitate                                                        0.196                                                                              0.188 (1)                                                                           0.514                                                                              1.44                                         Boiled, K.sub.3 [Fe(CN).sub.6 ] + 25 mol %                                    Ca.sub.2 [Fe(CN).sub.6 ]                               "Zn.sub.3 [Fe(CN).sub.6 ] .sub.2 "                                                       23  Rapid Mixing                                                                          Zn/Fe = 2.5, Tap H.sub.2 O, Precipitate                                                        0.160                                                                              0.152 (1)                                                                           0.532                                                                              1.13                                         Boiled, K.sub.3 [Fe(CN).sub.6 ] + 50 mol %                                    Ca.sub.2 [Fe(CN).sub.6 ]                               "Zn.sub.3 [Fe(CN).sub.6 ].sub.2 "                                                        24  Rapid Mixing                                                                          Zn/Fe = 2.5, Tap H.sub.2 O, Precipitate                                                        0.195                                                                              0.188 (1)                                                                           0.465                                                                              1.58                                         Boiled, K.sub.3 [Fe(CN).sub.6 ] + 10 mol %                                    Ca.sub.2 [Fe(CN).sub.6 ]                               "Zn.sub.2 [Fe(CN).sub.6 ]"                                                               25  Rapid Mixing                                                                          Zn/Fe = 4.25, Tap H.sub.2 O,                                                                   0.214                                                                              0.119 (10)                                                                          0.108                                                                              7.46                                         Ca.sub.2 [Fe(CN).sub.6 ] + 25 mol %                                           K.sub.3 [Fe(CN).sub.6 ]                                "Zn.sub.2 [Fe(CN).sub.6 ]"                                                               26  Rapid Mixing                                                                          Zn/Fe = 4.25, Tap H.sub.2 O,                                                                   0.236                                                                              0.092 (10)                                                                          0.039                                                                              22.8                                         Ca.sub.2 [Fe(CN).sub.6 ] + 10 mol %                                           K.sub.3 [Fe(CN).sub.6 ]                                "Zn.sub.2 [Fe(CN).sub.6 ]"                                                               27  Rapid Mixing                                                                          Zn/Fe = 4.25, Tap H.sub.2 O,                                                                   0.189                                                                              0.125 (10)                                                                          0.218                                                                              3.27                                         Ca.sub.2 [Fe(CN).sub.6 ] + 50 mol %                                           K.sub.3 [Fe(CN).sub.6 ]                                Al.sub.4 [Fe(CN).sub.6 ].sub.3                                                           28  Gelatinization                                                                        Al/Fe = 1.3 (Stoich. = 1.0),                                                                   0.045      0.022                                                                              7.7                                          De-Ionized H.sub.2 O                                   Ce.sub.4 [Fe(CN).sub.6 ].sub.3                                                           29  Slow Precipi-                                                                         Ce/Fe = 2.0 (Stoich. = 1.0),                                                                   0.013      0.031                                                                              1.6                                  tation  use Ca.sub.2 [Fe(CN).sub.6 ]                           Ce.sub.4 [Fe(CN).sub.6 ].sub.3                                                           30  Slow Precipi-                                                                         Ce/Fe = 2.0 (Stoich. = 1.0),                                                                   0.0        0.0                                       tation  use K.sub.4 [Fe(CN).sub.6 ]                            La.sub.4 [Fe(CN).sub.6 ].sub.3                                                           31  Slow Precipi-                                                                         La/Fe = 2.0 (Stoich. = 1.0),                                                                   0.0        0.0                                       tation  De-Ionized H.sub.2 O                                   Sn.sub.2 [Fe(CN).sub.6 ]                                                                 32  Rapid Mixing                                                                          Sn/Fe = 1.0 (Stoich. = 1.0),                                                                   0.012                                                                              0.007 (10)                                                                          0.02                                                                               1.2)                                         De-Ionized H.sub.2 O             (10 min)              Sn[Fe(CN).sub.6 ]                                                                        33  Rapid Mixing                                                                          Sn/Fe = 2.0 (Stoich. = 1.0),                                                                   0.010                                                                              0.002 (10)                                                                          0.004                                                                              9.4                                          De-Ionized H.sub.2 O                                   Cr[Fe(CN).sub.6 ]                                                                        34  Slow Precipi-                                                                         Cr/Fe = 2.0 De-Ionized H.sub.2 O                                                               0.0        0.0                                       tation                                                         La[Fe(CN).sub.6 ]                                                                        35  Slow Precipi-                                                                         La/Fe = 2.0, De-Ionized H.sub.2 O                                                              0.074                                                                              0.064 (10)                                                                          0.278                                                                              1.0                                  tation                                                         Pr[Fe(CN).sub.6 ]                                                                        36  Rapid Precipi-                                                                        Pr/Fe = 2.0, De-Ionized H.sub.2 O                                                              0.490                                                                              0.202 (10)                                                                          0.022                                                                              34.6                                 tation                              (10 min)                                                                           (10 min)              Pr[Fe(CN).sub.6 ]                                                                        37  Slow Precipi-                                                                         Pr/Fe 2                     0.034                                                                              23.2                                 tation                              (10 min)                                                                           (10 min)              Sc[Fe(CN).sub.6 ]                                                                        38  Slow Precipi-                                                                         Sc/Fe = 2.0, De-Ionized H.sub.2 O                                                              0.034                                                                              0.018 (10)                                                                          0.05 25.7                                 tation                                                         Y[Fe(CN).sub.6 ]                                                                         39  Rapid Precipi-                                                                        Y/Fe = 2.0, De-Ionized H.sub.2 O                                                               0.359                                                                              0.034 (10)                                                                          0.006                                                                              233                                  tation                                                         Y[Fe(CN).sub. 6 ]                                                                        40  Slow Precipi-                                                                         Y/Fe = 2.0, De-Ionized H.sub.2 O                                                               0.090                                                                              0.030 (10)                                                                          0.001                                                                              86.5                                 tation                   (100 min)  (10 min)                                                                           (10 min)              Ce[Co(CN).sub.6 ]                                                                        41  Slow Precipi-                                                                         Ce/Co = 2.0, De-Ionized H.sub.2 O                                                              0.527                                                                              0.201 0.012                                                                              64.7                                 tation                                   (10 min)              La[Co(CN).sub.6 ]                                                                        42  Slow Precipi-                                                                         La/Co = 2.0, De-Ionized H.sub.2 O                                                              0.030                                                                              0.022 (10)                                                                          0.068                                                                              1.67                                 tation                                                         __________________________________________________________________________

We claim:
 1. In a process for the separation of oxygen from a gas streamby adsorption, the improvement comprising using, as the adsorbent, acompound having the formula M_(x) [M'(CN)₆ ]_(y) wherein M is an elementhaving an atomic number of 21, 25 to 30, 39, 50, or 57 to 59; M' is anelement having an atomic number from 24 to 27; and x and y are positivewhole numbers such that the sum of the valence of M times x plus thevalence of [M'(CN)₆ ] times y is equal to zero.
 2. The process definedin claim 1 wherein the compound is

    Zn.sub.2 [Fe(CN).sub.6 ].


3. The process defined in claim 1 wherein the compound is

    Zn.sub.3 [Fe(CN).sub.6 ].sub.2.


4. The process defined in claim 1 wherein the compound is

    Co.sub.2 [Fe(CN).sub.6 ].


5. The process defined in claim 1 wherein the compound is

    Ce(III)[Fe(III)(CN).sub.6 ].